Automatic transmission

ABSTRACT

ECU instructed before the drive source ENG is determined to be in the stopped state, the control part ECU of the automatic transmission TM transmits a signal for switching a two-way clutch TW to a state corresponding to the state of a slider HC1.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application Ser.No. 2016-051478, filed on Mar. 15, 2016 and Japan application Ser. No.2017-045219, filed on Mar. 9, 2017. The entirety of each of theabove-mentioned patent applications is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an automatic transmission that includesplanetary gear mechanisms and engagement mechanisms.

Description of Related Art

Conventionally, an automatic transmission that includes planetary gearmechanisms having multiple elements rotatable inside a casing, andmultiple engagement mechanisms switchable to a coupled state in whichthe elements are coupled to one another, or switchable to a fixed statein which the elements are fixed to the casing has been known.

As one of the engagement mechanisms, it has been known that such anautomatic transmission uses a switching mechanism (a two-way clutch, forexample) that is switchable between the fixed state and the reverserotation preventing state which allows the normal rotation and preventsthe reverse rotation of the elements of the planetary gear mechanisms(refer to Patent Literature 1, for example).

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Publication No.    2015-230036.

SUMMARY OF THE INVENTION Problem to be Solved

The switching mechanism of a conventional automatic transmission such asone described in Patent Literature 1 is switched by a switching controlcircuit (a hydraulic pressure control circuit, for example). However,there is a case where the state of the switching mechanism which acontrol part has instructed to set and the actual state of the switchingmechanism do not match.

For example, under a configuration in which a hydraulic pressure controlcircuit is used as a switching control circuit and hydraulic pressure issupplied to the hydraulic pressure control circuit by an oil pump drivenby driving force from a drive source, the driving of the oil pump stopswhen the drive source is stopped. Therefore, there is a possibility thatan unexpected change to the hydraulic pressure supplied to the hydraulicpressure control circuit occurs and the state of the switching controlcircuit (and of the switching mechanism) becomes different from thestate instructed by the control part before the drive source is stopped.

Under such a circumstance, if the drive source is re-driven, theswitching control circuit may try to switch the switching mechanism tothe fixed state even if the differential rotation is occurring in theswitching mechanism. As a result, a large impact may be applied to thecomponents of the switching mechanism or the switching control circuit.

Solution to the Problem

The disclosure provides an automatic transmission with which a largeimpact is hardly applied to the components of the switching mechanism orthe switching control circuit when the drive source is re-driven.

An automatic transmission according to the disclosure includes an inputmember disposed inside a casing and rotated by driving force transmittedfrom a drive source, a planetary gear mechanism having a plurality ofelements rotatable inside the casing, and a plurality of engagementmechanisms switchable to a coupled state in which each of the elementsare coupled to one another or switchable to a fixed state in which theelements are fixed to the casing, an output member outputting rotation,and a control part controlling the engagement mechanisms and recognizingthe rotational frequency of the drive source. The automatic transmissionis capable of outputting the rotation of the input member to the outputmember while changing speed in a plurality of gear positions with theplanetary gear mechanism and the engagement mechanisms. The automatictransmission further includes a switching control circuit switching theengagement mechanisms according to a signal from the control part. Theplurality of engagement mechanisms includes a switching mechanismallowing the normal rotation and prevents the reverse rotation of thecorresponding element among the plurality of elements and switchablebetween a reverse rotation preventing state and the fixed state. Theswitching control part has a switching part switching the switchingmechanism to the reverse rotation preventing state and the fixed stateand a switching part state detector recognizing the state of theswitching part and transmitting a signal indicating the state of theswitching part to the control part. In the case where the drive sourceis determined to be in the stopped state by the control part, if thestate of the switching part does not correspond to the state instructedby the control part before the drive source is determined to be in thestopped state, the control part transmits a signal for switching theswitching mechanism to the state corresponding to the switching part.

When the control part of the automatic transmission according to thedisclosure determined that the drive source is in the stopped state, thecontrol part transmits a signal to the switching control circuit forswitching the switching mechanism to a state corresponding to the stateof the switching part if the state of the switching part does notcorrespond to the state instructed by the control part before the drivesource is determined to be in the stopped state. That is, the controlpart determines the actual state of the switching control circuit andinstructs the switching control part to correspond to the actual stateif the state which the control part has instructed and the actual stateare different.

Therefore, when the drive source is re-driven, the state of theswitching mechanism does not change because the actual state of theswitching part (that is, the actual state of the switching mechanism)matches with the state of the switching mechanism the control part hasinstructed. As a result, the switching mechanism is not forciblyswitched to the fixed state while the differential rotation isoccurring. Also, deterioration in the responsiveness of control afterre-driving the drive source is prevented.

Accordingly, the automatic transmission of the disclosure hardly causesbreakage and deterioration in the responsiveness when the drive sourceis re-driven.

Also, in the automatic transmission according to the disclosure, it ispreferable that the control part transmits a signal for switching theswitching mechanism to the reverse rotation preventing state to theswitching control circuit if the state of the switching part cannot berecognized in the case where the control part determined that the drivesource is in the stopped state.

By such a configuration, when the drive source is re-driven, drivingforce to forcibly switch the switching mechanism to the fixed state doesnot applied to the switching mechanism while the differential rotationis occurring in the switching mechanism regardless of whether the actualstate of the switching part corresponds to the fixed state or thereverse rotation preventing state.

Also, in the automatic transmission according to the disclosure, it ispreferable that the control part has a driving force detector detectingdriving force for changing the state of the switching part and transmitsa signal for switching the switching mechanism to the reverse rotationpreventing state to the switching control circuit if the driving forceis different from driving force corresponding to the state of theswitching mechanism in the case where the control part determined thatthe drive source is in the stopped state.

By such a configuration, when the drive source is re-driven, drivingforce to forcibly switch the switching mechanism to the fixed state doesnot applied to the switching mechanism while the differential rotationis occurring in the switching mechanism regardless of whether the actualstate of the switching part corresponds to the fixed state or thereverse rotation preventing state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of anautomatic transmission according to the embodiment.

FIG. 2 is a skeleton diagram of the automatic transmission of FIG. 1.

FIG. 3 is a collinear chart of the planetary gear mechanisms of theautomatic transmission.

FIG. 4 is a diagram describing the state of the engagement mechanisms ateach gear position of the automatic transmission.

FIG. 5 is a cross-sectional view illustrating the fixed state of thetwo-way clutch of the automatic transmission of FIG. 1.

FIG. 6 is a cross-sectional view illustrating the reverse rotationpreventing state of the principal part of the two-way clutch of theautomatic transmission of FIG. 1.

FIG. 7 is a perspective view illustrating the fixed state of the two-wayclutch of the automatic transmission of FIG. 1.

FIG. 8 is a perspective view illustrating the reverse rotationpreventing state of the two-way clutch of the automatic transmission ofFIG. 1.

FIGS. 9A and 9B are explanatory diagrams illustrating the hydraulicpressure control circuit performing switching of the two-way clutch ofthe automatic transmission of FIG. 1. FIG. 9A illustrates the case wherethe two-way clutch is switched to the fixed state, and FIG. 9Billustrates the case where the two-way clutch is switched to the reverserotation preventing state.

FIG. 10 is a flowchart illustrating the process performed when thecontrol part of the automatic transmission of FIG. 1 determines whetherthe drive source is stopped or not.

FIG. 11 is a flowchart illustrating the process performed when thecontrol part of the automatic transmission of FIG. 1 determines that thedrive source is stopped.

DESCRIPTION OF THE EMBODIMENTS

An automatic transmission according to an embodiment is describedhereinafter with reference to the drawings. The embodiment describes thecase where the automatic transmission is mounted on a vehicle, but theautomatic transmission according to the disclosure may be mounted onother vehicles such as a vessel or an unmanned machine.

Firstly, referring to FIGS. 1 and 2, the schematic configuration of anautomatic transmission TM is described. FIG. 1 is schematic diagramillustrating a configuration of the automatic transmission TM. FIG. 2 isa skeleton diagram of the automatic transmission TM.

As shown in FIG. 1, the automatic transmission TM includes atransmission case 1 (casing), an input shaft 2 (input member) pivotallysupported to be rotatable inside the transmission case 1 and an outputgear 3 (output member) pivotally supported to be rotatableconcentrically with the input shaft 2 inside the transmission case 1.

Also, the vehicle on which the automatic transmission TM is mountedincludes a shift lever SL capable of switching the shift position to anyof the forward range, the neutral range and the reverse range, anaccelerator opening detector 4 detecting the on/off state of anaccelerator pedal AP, and a brake pedal detector 5 detecting the on/offstate of a brake pedal BP.

As shown in FIG. 2, driving force output by a drive source ENG such asan internal combustion engine (engine) is transmitted to the input shaft2 via a torque converter TC. The torque converter TC has a lock-upclutch LC and a dumper DA. A start clutch of a single-plate type or amulti-plate type configured to be frictionally engageable may bedisposed instead of the torque converter TC.

The rotation of the output gear 3 is transmitted to driving wheelsdisposed on the left and right sides of the vehicle via a differentialgear (not depicted) or a propeller shaft (not depicted).

Inside the transmission case 1, four planetary gear mechanisms, whichare the first planetary gear mechanism PGS1, the second planetary gearmechanism PGS2, the third planetary gear mechanism PGS3 and the fourthplanetary gear mechanism PGS4, are disposed concentrically with theinput shaft 2.

Also, seven engagement mechanisms, which are the first clutch C1, thesecond clutch C2, the third clutch C3, the first brake B1, the secondbrake B2, the third brake B3 and the fourth brake B4, are disposedinside the transmission case 1.

Next, referring to FIG. 3, the four planetary gear mechanisms and theseven engagement mechanisms included in the automatic transmission TMare described.

A collinear chart (a chart that can indicate the relative rotationalspeed ratio of three elements of the planetary gear mechanism asstraight lines (velocity diagram)) in FIG. 3 indicates the collinearchart of the second planetary gear mechanism PGS2, of the firstplanetary gear mechanism PGS1, of the third planetary gear mechanismPGS3 and of the fourth planetary gear mechanism PGS4, in order from thetop of the chart.

The first planetary gear mechanism PGS1 is constituted with a so-calledplanetary gear mechanism of a single pinion type including a sun gearSa, a ring gear Ra and a carrier Ca that pivotally supports a pinion Paengaging with the sun gear Sa and the ring gear Ra to be rotatable andrevoluvable.

A planetary gear mechanism of a single pinion type such as the planetarygear mechanism PGS1 is also called as a minus planetary gear mechanismor a negative planetary gear mechanism because the ring gear rotates inthe different direction to the sun gear when the sun gear is rotatedwhile the carrier is fixed. In this planetary gear mechanism, thecarrier and the sun gear rotate in the same direction when the sun gearis rotated while the ring gear is fixed.

As shown in the second section from the top of the collinear chart inFIG. 3, if the three elements, Sa, Ca and Ra, of the first planetarygear mechanism PGS1 are indicated as the first element, the secondelement and the third element respectively from the left (a side) in theorder of the intervals corresponding to the gear ratios (the number ofteeth of the ring gear/the number of teeth of the sun gear) in thecollinear chart, the first element is the sun gear Sa, and the secondelement is the carrier Ca, and the third element is the ring gear Ra.

The ratio of the interval between the sun gear Sa and the carrier Ca andthe interval between the carrier Ca and the ring gear Ra is set to h:1as h indicates the gear ratio of the first planetary gear mechanismPGS1.

The second planetary gear mechanism PGS2 is also constituted with aso-called planetary gear mechanism of a single pinion type including asun gear Sb, a ring gear Rb and a carrier Cb that pivotally supports apinion Pb engaging with the sun gear Sb and the ring gear Rb to berotatable and revoluvable, as the same as the first planetary gearmechanism PGS1.

As shown in the first (uppermost) section from the top of the collinearchart in FIG. 3, if the three elements, Sb, Cb and Rb, of the secondplanetary gear mechanism PGS2 are indicated as the fourth element, thefifth element and the sixth element respectively from the left (a side)in the order of the intervals corresponding to the gear ratios in thecollinear chart, the fourth element is the ring gear Rb, and the fifthelement is the carrier Cb, and the sixth element is the sun gear Sb.

The ratio of the interval between the sun gear Sb and the carrier Cb andthe interval between the carrier Cb and the ring gear Rb is set to i:1as i indicates the gear ratio of the second planetary gear mechanismPGS2.

The third planetary gear mechanism PGS3 is also constituted with aso-called planetary gear mechanism of a single pinion type including asun gear Sc, a ring gear Rc and a carrier Cc that pivotally supports apinion Pc engaging with the sun gear Sc and the ring gear Rc to berotatable and revoluvable, as the same as the first planetary gearmechanism PGS1 and the second planetary gear mechanism PGS2.

As shown in the third section from the top of the collinear chart inFIG. 3, if the three elements, Sc, Cc and Re, of the third planetarygear mechanism PGS3 are indicated as the seventh element, the eighthelement and the ninth element respectively from the left (a side) in theorder of the intervals corresponding to the gear ratios in the collinearchart, the seventh element is the sun gear Sc, and the eighth element isthe carrier Cc, and the ninth element is the ring gear Re.

The ratio of the interval between the sun gear Sc and the carrier Cc andthe interval between the carrier Cc and the ring gear Rc is set to j:1as j indicates the gear ratio of the third planetary gear mechanismPGS3.

The fourth planetary gear mechanism PGS4 is also constituted with aso-called planetary gear mechanism of a single pinion type including asun gear Sd, a ring gear Rd and a carrier Cd that pivotally supports apinion Pd engaging with the sun gear Sd and the ring gear Rd to berotatable and revoluvable, as the same as the first planetary gearmechanism PGS1, the second planetary gear mechanism PGS2 and the thirdplanetary gear mechanism PGS3.

As shown in the fourth (lowermost) section from the top of the collinearchart in FIG. 3, if the three elements, Sd, Cd and Rd, of the fourthplanetary gear mechanism PGS4 are indicated as the tenth element, theeleventh element and the twelfth element respectively from the left inthe order of the intervals corresponding to the gear ratios in thecollinear chart, the tenth element is the ring gear Rd, and the eleventhelement is the carrier Cd, and the twelfth element is the sun gear Sd.

The ratio of the interval between the sun gear Sd and the carrier Cd andthe interval between the carrier Cd and the ring gear Rd is set to k:1as k indicates the gear ratio of the fourth planetary gear mechanismPGS4.

The sun gear Sa (the first element) of the first planetary gearmechanism PGS1 is coupled to the input shaft 2 (input member). The ringgear Rd (the tenth element) of the fourth planetary gear mechanism PGS4is coupled to the output gear 3 (output member).

Also, the carrier Ca (the second element) of the first planetary gearmechanism PGS1, the carrier Cb (the fifth element) of the secondplanetary gear mechanism PGS2 and the ring gear Rc (the ninth element)of the third planetary gear mechanism PGS3 are coupled and constitutethe first coupled body Ca-Cb-Rc. The ring gear Ra (the third element) ofthe first planetary gear mechanism PGS1 and the sun gear Sd (the twelfthelement) of the fourth planetary gear mechanism PGS4 are coupled andconstitute the second coupled body Ra-Sd. The carrier Cc (the eighthelement) of the third planetary gear mechanism PGS3 and the carrier Cd(the eleventh element) of the fourth planetary gear mechanism PGS4 arecoupled and constitute the third coupled body Cc-Cd.

The first clutch C1 is a wet multiple-disk friction clutch of ahydraulic actuation type. The first clutch C1 is configured to beswitchable between the coupled state in which the sun gear Sa (the firstelement) of the first planetary gear mechanism PGS1 and the thirdcoupled body Cc-Cd are coupled and the released state in which the sungear Sa and the third coupled body Cc-Cd are uncoupled.

The second clutch C2 is a wet multiple-disk friction clutch of ahydraulic actuation type. The second clutch C2 is configured to beswitchable between the coupled state in which the sun gear Sa (the firstelement) of the first planetary gear mechanism PGS1 and the ring gear Rb(the fourth element) of the second planetary gear mechanism PGS2 arecoupled and the released state in which the sun gear Sa and the ringgear Rb are uncoupled.

The third clutch C3 is a wet multiple-disk friction clutch of ahydraulic actuation type. The third clutch C3 is configured to beswitchable between the coupled state in which the sun gear Sb (the sixthelement) of the second planetary gear mechanism PGS2 and the secondcoupled body Ra-Sd are coupled and the released state in which the sungear Sb and the second coupled body Ra-Sd are uncoupled.

The first brake B1 is a so-called two-way clutch. The first brake B1 isconfigured to be switchable between the reverse rotation preventingstate which allows the normal rotation (the rotation in the samedirection as the rotational direction of the input shaft 2) and preventsthe reverse rotation of the third coupled body Cc-Cd and the fixed statein which the third coupled body Cc-Cd is fixed to the transmission case1.

In the reverse rotation preventing state, the rotation of the firstbrake B1 is allowed when the force to rotate the third coupled bodyCc-Cd in the normal direction is applied, and the rotation of the firstbrake B1 is prevented and the first brake B1 is fixed to thetransmission case 1 when the force to rotate the third coupled bodyCc-Cd in the reverse direction is applied.

In the fixed state, the rotation of the first brake B1 is prevented andthe first brake B1 is fixed to the transmission case 1 in either casewhere the force to rotate the third coupled body Cc-Cd in the normaldirection or in the reverse direction is applied.

The second brake B2 is a wet multiple-disk friction brake of a hydraulicactuation type. The second brake B2 is configured to be switchablebetween the fixed state in which the sun gear Sc (the seventh element)of the third planetary gear mechanism PGS3 is fixed to the transmissioncase 1 and the released state in which the sun gear Sc is released fromthe transmission case 1.

The third brake B3 is a wet multiple-disk friction brake of a hydraulicactuation type. The third brake B3 is configured to be switchablebetween the fixed state in which the sun gear SU (the sixth element) ofthe second planetary gear mechanism PGS2 is fixed to the transmissioncase 1 and the released state in which the sun gear SU is released fromthe transmission case 1.

The fourth brake B4 is an engagement mechanism constituted with a dogclutch or a synchromesh mechanism having a synchronization function. Thefourth brake B4 is configured to be switchable between the fixed statein which the ring gear Rb (the fourth element) of the second planetarygear mechanism PGS2 is fixed to the transmission case 1 and the releasedstate in which the ring gear Rb is released from the transmission case1.

The control part ECU (refer to FIG. 1) including a transmission controlunit switches the state of the first clutch C1, the second clutch C2,the third clutch C3, the first brake B1, the second brake B2, the thirdbrake B3 and the fourth brake B4 based on vehicle information such asthe travelling speed of the vehicle.

As shown in FIG. 2, the second clutch C2, the second planetary gearmechanism PGS2, the third clutch C3, the output gear 3, the firstplanetary gear mechanism PGS1, the first clutch C1 and the thirdplanetary gear mechanism PGS3 are disposed on the axis line of the inputshaft 2 in this order from the side of the driving source ENG and thetorque converter TC.

The fourth brake B4 is disposed outside in the radial direction of thesecond planetary gear mechanism PGS2. The third brake B3 is disposedoutside in the radial direction of the third clutch C3. The first brakeB1 is disposed outside in the radial direction of the first clutch C1.The second brake B2 is disposed outside in the radial direction of thethird planetary gear mechanism PGS3.

As such, in the automatic transmission TM, the axial length of theautomatic transmission is shortened by disposing the four brakes outsidein the radial direction of the planetary gear mechanisms or theclutches, compared to an automatic transmission disposing the brakes onthe axis line of the input shaft 2 together in line with the planetarygear mechanisms and the clutches. The fourth brake B4 may be disposedoutside in the radial direction of the second clutch C2, and the thirdbrake B3 may be disposed outside in the radial direction of the secondplanetary gear mechanism PGS2.

Also, the fourth planetary gear mechanism PGS4 is disposed outside inthe radial direction of the first planetary gear mechanism PGS1. Thering gear Ra (the third element) of the first planetary gear mechanismPGS1 and the sun gear Sd (the twelfth element) of the fourth planetarygear mechanism PGS4 are integrally coupled and constitute the secondcoupled body Ra-Sd.

As such, in the automatic transmission TM, the axial length of theautomatic transmission is shortened by disposing the fourth planetarygear mechanism PGS4 outside in the radial direction of the firstplanetary gear mechanism PGS1 so that the first planetary gear mechanismPGS1 and the fourth planetary gear mechanism PGS4 are overlapped in theradial direction.

The axial length can be shortened when the first planetary gearmechanism PGS1 and the fourth planetary gear mechanism PGS4 areoverlapped at least partially in the radial direction, and the axiallength can be shortest when both the first planetary gear mechanism PGS1and the fourth planetary gear mechanism PGS4 are completely overlappedin the radial direction.

Next, referring to FIGS. 3 and 4, the state of the engagement mechanisms(that is, the first clutch C1, the second clutch C2, the third clutchC3, the first brake B1, the second brake B2, the third brake B3 and thefourth brake B4) when each gear position is established in the automatictransmission TM is described.

In the collinear chart of FIG. 3, the lower horizontal line and theupper horizontal line in each section (for example, the line overlappedwith the collinear line 4th and 6th in the first planetary gearmechanism PGS1 in the second section from the top of the FIG. 3)respectively indicate the rotational speed of “0” and “1” (the samerotational speed as the input shaft 2, which is the input member).

Also, in the collinear chart of FIG. 3, the velocity diagram illustratedby broken lines indicates that each element of the planetary gearmechanisms other than the planetary gear mechanism transmitting poweramong the first planetary gear mechanism

PGS1, the second planetary gear mechanism PGS2, the third planetary gearmechanism PGS3 and the fourth planetary gear mechanism PGS4 rotates(idles) following the planetary gear mechanism transmitting power.

The table shown as FIG. 4 summarizes the states of the engagementmechanisms at each gear position, and the symbol “0” indicates that theengagement mechanism of the corresponding column is in the coupled stateor the fixed state, and absence of the symbol indicates that theengagement mechanism of the corresponding column is in the releasedstate.

In FIG. 4, “R” in the column of the first brake B1 indicates that thefirst brake B1 is in the reverse rotation preventing state, and “F” inthe same column indicates that the first brake B1 is in the fixed state.

In FIG. 4, “R” with the underline indicates that the rotational speed ofthe third coupled body Cc-Cd or the sun gear Sc (the seventh element) ofthe third planetary gear mechanism PGS3 becomes “0” by the operation ofthe first brake B1. Also, “R/F” indicates that it is “R”, which means inthe reverse rotation preventing state in the usual condition butswitched to “F”, which means in the fixed state or the normal rotationpreventing state, when applying the engine braking.

As shown in FIG. 4, when establishing the first gear position in theautomatic transmission TM the first brake B1, which is a two-way clutch,is set to the reverse rotation preventing state, and sets the secondbrake B2 and the third brake B3 is set to the fixed state.

By setting the first brake B1 to the reverse rotation preventing state,the reverse rotation of the third coupled body Cc-Cd and the sun gear Sc(the seventh element) of the third planetary gear mechanism PGS3 isprevented, and the rotational speed of the third coupled body Cc-Cd andthe sun gear Sc (the seventh element) of the third planetary gearmechanism PGS3 becomes “0”. Then, the sun gear Sc (the seventh element),the carrier Cc (the eighth element) and the ring gear Rc (the ninthelement) of the third planetary gear mechanism PGS3 become in the lockedstate in which these elements cannot relatively rotate, and therotational speed of the first coupled body Ca-Cb-Rc, which includes thering gear Rc (the ninth element) of the third planetary gear mechanismPGD3, also becomes “0”.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “1st” shown in FIG. 3, and the first gear position isestablished. To apply the engine braking at the first gear position, thefirst brake B1 may be switched to the fixed state.

It is not necessary to set the third brake B3 to the fixed state toestablish the first gear position. However, the third brake B3 is set tothe fixed state here for smoothly shifting from the first gear positionto the second gear position described below.

To establish the second gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thesecond brake B2 and the third brake B3 are set to the fixed state, andthe third clutch C3 is set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the second brake B2 to the fixed state, the rotational speed ofthe sun gear Sc (the seventh element) of the third planetary gearmechanism PGS3 becomes “0”. By setting the third brake B3 to the fixedstate, the rotational speed of the sun gear Sb (the sixth element) ofthe second planetary gear mechanism PGS2 becomes “0”.

By setting the third clutch C3 to the coupled state, the rotationalspeed of the second coupled body Ra-Sd becomes “0”, which is the same asthe rotational speed of the sun gear SU (the sixth element) of thesecond planetary gear mechanism PGS2.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “2nd” shown in FIG. 3, and the second gear position isestablished.

To establish the third gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thesecond brake B2 and the third brake B3 are set to the fixed state, andthe second clutch C2 is set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the second brake B2 to the fixed state, the rotational speed ofthe sun gear Sc (the seventh element) of the third planetary gearmechanism PGS3 becomes “0”. By setting the third brake B3 to the fixedstate, the rotational speed of the sun gear Sb (the sixth element) ofthe second planetary gear mechanism PGS2 becomes “0”.

By setting the second clutch C2 to the coupled state, the rotationalspeed of the ring gear Rb (the fourth element) of the second planetarygear mechanism PGS2 becomes “1”, which is the same as the rotationalspeed of the sun gear Sa (the first element) of the first planetary gearmechanism PGS1 coupled to the input shaft 2. The rotational speed of thecarrier Cb (the fifth element), that is, the rotational speed of thefirst coupled body Ca-Cb-Rc becomes i/(i30 1) because the rotationalspeed of the sun gear Sb (the sixth element) of the second planetarygear mechanism PGS2 becomes “0” and the rotational speed of the ringgear Rb (the fourth element) becomes “1”.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “3rd” shown in FIG. 3, and the third gear position isestablished.

To establish the fourth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thesecond brake B2 is set to the fixed state, and the second clutch C2 andthe third clutch C3 are set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the second brake B2 to the fixed state, the rotational speed ofthe sun gear Sc (the seventh element) of the third planetary gearmechanism PGS3 becomes “0”.

By setting the third clutch C3 to the coupled state, the sun gear Sb(the sixth element) of the second planetary gear mechanism PGS2 and thesecond coupled body Ra-Sd rotate at the same speed. At this time, thecarrier Ca (the second element) and the carrier Cb (the fifth element)are coupled, and the ring gear Ra (the third element) and the sun gearSb (the sixth element) are coupled between the first planetary gearmechanism PGS1 and the second planetary gear mechanism PGS2. Therefore,in the fourth gear position which sets the third clutch C3 to thecoupled state, a single collinear chart consisting of four elements canbe depicted for the first planetary gear mechanism PGS1 and the secondplanetary gear mechanism PGS2.

By setting the second clutch C2 to the coupled state, the rotationalspeed of the ring gear Rb (the fourth element) of the second planetarygear mechanism PGS2 becomes “1”, which is the same as the rotationalspeed of the sun gear Sa (the first element) of the first planetary gearmechanism PGS1, and the rotational speed of two elements out of the fourelements constituting the first planetary gear mechanism PGS1 and thesecond planetary gear mechanism PGS2 becomes “1”. Accordingly, each ofthe elements of the first planetary gear mechanism PGS1 and the secondplanetary gear mechanism PGS2 becomes in the locked state in which theseelements cannot relatively rotate, and the rotational speed of all theelements of the first planetary gear mechanism PGS1 and the secondplanetary gear mechanism PGS2 becomes “1”.

Thereby, the rotational speed of the third coupled body Cc-Cd becomesj/(j+1) and the rotational speed of the ring gear Rd (the tenth element)of the fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “4th” shown in FIG. 3, and the fourth gear position isestablished.

To establish the fifth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thesecond brake B2 is set to the fixed state, and the first clutch C1 andthe second clutch C2 are set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the second brake B2 to the fixed state, the rotational speed ofthe sun gear Sc (the seventh element) of the third planetary gearmechanism PGS3 becomes “0”.

By setting the first clutch C1 to the coupled state, the rotationalspeed of the third coupled body Cc-Cd becomes “1”, which is the same asthe rotational speed of the sun gear Sa (the first element) of the firstplanetary gear mechanism PGS1.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “5th” shown in FIG. 3, and the fifth gear position isestablished.

It is not necessary to set the second clutch C2 to the coupled state toestablish the fifth gear position. However, because the second clutch C2needs to be set to the coupled state in the fourth gear position and thesixth gear position, which is described later, the second clutch C2 isset to the coupled state here in the fifth gear position for smoothlydownshifting from the fifth gear position to the fourth gear position orupshifting from the fifth gear position to the sixth gear positiondescribed below.

To establish the sixth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, and thefirst clutch C1, the second clutch C2 and the third clutch C3 are set tothe coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed.

By setting the second clutch C2 and the third clutch C3 to the coupledstate, as described in the fourth gear position, each of the elements ofthe first planetary gear mechanism PGS1 and the second planetary gearmechanism PGS2 becomes in the locked state in which these elementscannot relatively rotate, and the rotational speed of the second coupledbody Ra-Sd becomes. By setting the first clutch C1 to the coupled state,the rotational speed of the third coupled body Cc-Cd becomes “1”.Accordingly, in the fourth planetary gear mechanism PGS4, the carrier Cd(the eleventh element) and the sun gear Sd (the twelfth element) becomethe same speed of “1” and become in the locked state in which theseelements cannot relatively rotate.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “1” as “6th” shown in FIG. 3, and the sixth gear position isestablished.

To establish the seventh gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thethird brake B3 is set to the fixed state, and the first clutch C1 andthe second clutch C2 are set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the third brake B3 to the fixed state, the rotational speed ofthe sun gear Sb (the sixth element) of the second planetary gearmechanism PGS2 becomes “0”.

By setting the second clutch C2 to the coupled state, the rotationalspeed of the ring gear Rb (the fourth element) of the second planetarygear mechanism PGS2 becomes “1”, which is the same as the rotationalspeed of the sun gear Sa (the first element) of the first planetary gearmechanism PGS1, and the rotational speed of the first coupled bodyCc-Cb-Rc, which includes the carrier Cb (the fifth element) of thesecond planetary gear mechanism PGS2, becomes i/(i+1). By setting thefirst clutch C1 to the coupled state, the rotational speed of the thirdcoupled body Cc-Cd becomes “1”, which is the same as the rotationalspeed of the sun gear Sa (the first element) of the first planetary gearmechanism PGS1 coupled to the input shaft 2.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “7th” shown in FIG. 3, and the seventh gear position isestablished.

To establish the eighth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thethird brake B3 is set to the fixed state, and the first clutch C1 andthe third clutch C3 are set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the third brake B3 to the fixed state, the rotational speed ofthe sun gear Sb (the sixth element) of the second planetary gearmechanism PGS2 becomes “0”.

By setting the third clutch C3 to the coupled state, the rotationalspeed of the second coupled body Ra-Sd becomes “0”, which is the same asthe rotational speed of the sun gear Sb (the sixth element) of thesecond planetary gear mechanism PGS2. Also, by setting the first clutchC1 to the coupled state, the rotational speed of the third coupled bodyCc-Cd becomes “1”, which is the same as the rotational speed of the sungear Sa (the first element) of the first planetary gear mechanism PGS1.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “8th” shown in FIG. 3, and the eighth gear position isestablished.

To establish the ninth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thethird brake B3 and the fourth brake B4 are set to the fixed state, andthe first clutch C1 is set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the third brake B3 to the fixed state, the rotational speed ofthe sun gear Sb (the sixth element) of the second planetary gearmechanism PGS2 becomes “0”. By setting the fourth brake B4 to the fixedstate, the rotational speed of the ring gear Rb (the fourth element) ofthe second planetary gear mechanism PGS2 also becomes “0”. Therefore,each of the elements Sb, Cb and Rb of the second planetary gearmechanism PGS2 becomes in the locked state in which these elementscannot relatively rotate, and the rotational speed of the first coupledbody Ca-Cb-Rc, which includes the carrier Cb (the fifth element) of thesecond planetary gear mechanism PGS2, also becomes “0”.

By setting the first clutch C1 to the coupled state, the rotationalspeed of the third coupled body Cc-Cd becomes “1”, which is the same asthe rotational speed of the sun gear Sa (the first element) of the firstplanetary gear mechanism PGS1.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “9th” shown in FIG. 3, and the ninth gear position isestablished.

To establish the tenth gear position, the first brake B1, which is atwo-way clutch, is set to the reverse rotation preventing state, thefourth brake B4 is set to the fixed state, and the first clutch C1 andthe third clutch C3 are set to the coupled state.

By setting the first brake B1 to the reverse rotation preventing state,the normal rotation of the third coupled body Cc-Cd is allowed. Bysetting the fourth brake B4 to the fixed state, the rotational speed ofthe ring gear Rb (the fourth element) of the second planetary gearmechanism PGS2 becomes “0”.

By setting the third clutch C3 to the coupled state, the second coupledbody Ra-Sd and the sun gear Sb (the sixth element) of the secondplanetary gear mechanism PGS2 rotate at the same speed. Also, by settingthe first clutch C1 to the coupled state, the rotational speed of thethird coupled body Cc-Cd becomes “1”, which is the same as therotational speed of the sun gear Sa (the first element) of the firstplanetary gear mechanism PGS1.

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “10th” shown in FIG. 3, and the tenth gear position isestablished.

To establish the reverse gear position, the first brake B1, which is atwo-way clutch, and the third brake B3 are set to the fixed state, andthe second clutch C2 is set to the coupled state.

By setting the first brake B1 to the fixed state, the rotational speedof the third coupled body Cc-Cd becomes “0”. Also, by setting the thirdbrake B3 to the fixed state and the second clutch C2 to the coupledstate, the rotational speed of the first coupled body Ca-Cb-Rc becomesi/(i+1).

Thereby, the rotational speed of the ring gear Rd (the tenth element) ofthe fourth planetary gear mechanism PGS4 coupled to the output gear 3becomes “Rvs” which is reverse rotation shown in FIG. 3, and the reversegear position is established.

FIG. 4 also indicates the change gear ratio (the rotational speed of theinput shaft 2/the rotational speed of the output gear 3) correspondingto each gear position in the case where the gear ratio h of the firstplanetary gear mechanism PGS1 is 2.734, the gear ratio i of the secondplanetary gear mechanism PGS2 is 1.614, the gear ratio j of the thirdplanetary gear mechanism PGS3 is 2.681, and the gear ratio k of thefourth planetary gear mechanism PGS4 is 1.914, and the common ratio (theratio of the change gear ratio between each gear position, calculated bydividing the change gear ratio corresponding to a predetermined gearposition by the change gear ratio of a gear position that is oneposition higher speed side than the predetermined gear ratio). Accordingto these ratios, it is understood that the common ratio can beadequately set.

Next, referring to FIGS. 5 to 8, an example of the two-way clutch usedas the first brake B1 (the switching mechanism) in the automatictransmission TM is described.

The first brake B1 is constituted with a two-way clutch switchablebetween the fixed state in which the third coupled body Cc-Cd is fixedto the transmission case 1 and the reverse rotation preventing statewhich allows the normal rotation and prevents the reverse rotation ofthe third coupled body Cc-Cd. A two-way clutch TW with the configurationshown in FIGS. 5 to 8 is used as such a two-way clutch.

As shown in the cross-sectional views of FIGS. 5 and 6, the two-wayclutch TW includes a fixed plate TW1 fixed to the transmission case 1and a rotating plate TW2 coupled to the third coupled body Cc-Cd.

As shown in FIGS. 7 and 8, the fixed plate TW1 is formed into an annularshape (donut shape). The rotating plate TW2, omitted in FIGS. 7 and 8,is also formed into an annular shape (donut shape) similar to the fixedplate TW1. The fixed plate TW1 and the rotating plate TW2 areconcentrically disposed.

As shown in FIG. 5, the first housing portion TW1 b and the secondhousing portion TW1 c are formed as recesses on a counter surface TW1 aof the fixed plate TW1 facing the rotating plate TW2. A plate-shapednormal rotation preventing member TW3 is storably disposed to the firsthousing portion TW1 b. A plate-shaped reverse rotation preventing memberTW4 is storably disposed to the second housing portion TW1 c.

An end portion of the normal rotation preventing member TW3 on the otherside in the peripheral direction (the direction in which the rotatingplate TW2 reversely rotates) is a swing end portion TW3 a. The swing endportion TW3 a is swingable with an end portion on the peripheraldirection side (the direction in which the rotating plate TW2 isnormally rotates) as a pivot.

An end portion of the reverse rotation preventing member TW4 on heperipheral direction side (the direction in which the rotating plate TW2normally rotates) is a swing end portion TW4 a. The swing end portionTW4 a is swingable with an end portion on the other side in theperipheral direction (the direction in which the rotating plate TW2 isreversely rotates) as a pivot.

The first spring TW5 is disposed between the bottom surface of the firsthousing portion TW1 b and the normal rotation preventing member TW3. Thefirst spring TW5 energizes the swing end portion TW3 a of the normalrotation preventing member TW3 so that the swing end portion TW3 a isprotruded from the first housing portion TW1 b.

The second spring TW6 is disposed between the bottom surface of thesecond housing portion TW1 c and the reverse rotation preventing memberTW4. The second spring TW6 energizes the swing end portion TW4 a of thereverse rotation preventing member TW4 so that the swing end portion TW4a is protruded from the second housing portion TW1 c.

The first recess TW2 b is disposed at the location corresponding to thenoiival rotation preventing member TW3 on a counter surface TW2 a of therotating plate TW2 facing the fixed plate TW1. The second recess TW2 cis disposed at the location corresponding to the reverse rotationpreventing member TW4 on the counter surface TW2 a of the rotating plateTW2.

The first engagement portion TW2 d is disposed on the first recess TW2 bon the other side in the peripheral direction (reverse rotationdirection side) of the rotating plate TW2. The first engagement portionTW2 d is formed into a stage shape engageable with the swing end portionTW3 a of the normal rotation preventing member TW3.

The second engagement portion TW2 e is disposed on the first recess TW2c on the peripheral direction side (normal rotation direction side) ofthe rotating plate TW2. The second engagement portion TW2 e is formedinto a stage shape engageable with the swing end portion TW4 a of thereverse rotation preventing member TW4.

As shown in FIGS. 5 and 7, both the normal rotation and the reverserotation of the rotating plate TW2 are prevented when the swing endportion TW3 a of the normal rotation preventing member TW3 and the firstengagement portion TW2 d are in the engageable state, and the swing endportion TW4 a of the reverse rotation preventing member TW4 and thesecond engagement portion TW2 e are in the engageable state.

Accordingly, the fixed state in the two-way clutch TW is the state inwhich the swing end portion TW3 a is engaged with the correspondingfirst engagement portion TW2 d and the swing end portion TW4 a isengaged with the corresponding second engagement portion TW2 e.

A switching plate TW7 is sandwiched between the fixed plate TW1 and therotating plate TW2. As show in FIGS. 7 and 8, the switching plate TW7 isalso formed into an annular shape (donut shape). The first notch holesTW7 a and the second notch holes TW7 b are disposed on the switchingplate TW7 at the locations corresponding to the normal rotationpreventing member TW3 and the reverse rotation preventing member TW4.

A protrusion TW7 c protruding outward in the radial direction isdisposed on the outer rim of the switching plate TW7. As shown in FIG.8, the switching plate TW7 is swingable with respect to the fixed plateTW1.

The first notch holes TW7 a corresponding to the normal rotationpreventing members TW3 move in the circumferential direction from thepositions corresponding to the normal rotation preventing members TW3when the switching plate TW7 is swung from the fixed state shown in FIG.7 to the state shown in FIG. 8. Therefore, the normal rotationpreventing members TW3 are pushed by the switching plate TW7 and housedinside the first housing portion TW1 b while opposing the energizingforce of the first spring TW5 (refer to FIG. 6). Thereby, the engagementof the swing end portion TW3 a of the normal rotation preventing membersTW3 and the first engagement portion TW2 d is prevented. Accordingly,the rotation of the rotating plate TW2 to the normal rotation side isallowed.

On the contrary, the second notch holes TW7 b corresponding to thereverse rotation preventing members TW4 remain at the positionscorresponding to the reverse rotation preventing members TW4 even theswitching plate TW7 is swung from the fixed state shown in FIG. 7 to thestate shown in FIG. 8. Therefore, the reverse rotation preventingmembers TW4 are not pushed by the switching plate TW7 and protruded fromthe second housing portions TW1 c by the energizing force of the secondsprings TW6 (refer to FIG. 5). Thereby, the swing end portion TW4 a ofthe reverse rotation preventing members TW4 is engaged with the secondengagement portion

TW2 e. Accordingly, the rotation of the rotating plate TW2 to thereverse rotation side is prevented.

The reverse rotation preventing state in the two-way clutch TW is thestate in which the rotation of the rotating plate TW2 to the normalrotation side is allowed and the rotation to the reverse rotation sideis prevented in the abovementioned manner.

Also, the second notch holes TW7 b corresponding to the reverse rotationpreventing members TW4 move from the positions corresponding to thereverse rotation preventing members TW4 to the circumferential directionwhen the switching plate TW7 is moved from the position indicated withthe two-dot dashed line in FIG. 8 to further the normal rotation side.Therefore, the reverse rotation preventing members

TW4 are pushed by the switching plate TW7 and housed inside the secondhousing portions TW1 c while opposing to the energizing force of thesecond springs TW6. Thereby, the engagement of the swing end portion TW4a of the reverse rotation preventing member TW4 and the secondengagement portion TW2 e is prevented. Accordingly, the rotation of therotating plate TW2 to the reverse rotation side is allowed.

On the contrary, the first notch holes TW7 a corresponding to the normalrotation preventing members TW3 remain at the position corresponding tothe normal rotation preventing members TW3 even the switching plate TW7is moved from the position indicated with the two-dot dashed line inFIG. 8 to further the normal rotation side. Therefore, the normalrotation preventing members TW3 are not pushed by the switching plateTW7 and protruded from the first housing portion TW1 b by the energizingforce of the first springs TW5 (refer to FIG. 5). Thereby, the swing endportion TW3 a of the normal rotation preventing member TW3 is engagedwith the first engagement portion TW2 d. Accordingly, the rotation ofthe rotating plate TW2 to the normal rotation side is prevented.

The normal rotation preventing state in the two-way clutch TW is thestate in which the rotation of the rotating plate TW2 to the reverserotation side is allowed and the rotation to the normal rotation side isprevented in the abovementioned manner.

Next, referring to FIGS. 9A and 9B, an example of the switching controlcircuit for switching the engagement mechanisms according to signalsfrom the control part ECU is described.

As shown in FIGS. 9A and 9B, a hydraulic pressure control circuit HCincludes a slider HC1 engaging with the protrusion TW7 c disposed on theswitching plate TW7. When the slider HC1 is positioned on the right sideof FIGS. 9A and 9B, the two-way clutch TW is switched to the reverserotation preventing state. When the slider HC1 is positioned on the leftside of FIGS. 9A and 9B, the two-way clutch TW is switched to the fixedstate.

The right side of the slider HC1 on the drawing is configured to be ableto supply line pressure via the first valve HC2 constituted with asolenoid valve. The left side of the slider HC1 on the drawing isconfigured to be able to supply line pressure via the second valve HC3constituted with a solenoid valve. The first valve HC2 is of a normalclosed type, and the second valve HC3 is of a normal opened type.

The first valve HC2 and the second valve HC3 are opened and closedaccording to the signals from the control part ECU. That is, the two-wayclutch TW is controlled by the control part ECU via the hydraulicpressure control circuit HC.

Hydraulic pressure supplied to the second clutch C2 is supplied to theright side of the slider HC1 on the drawing on a different surface fromthe surface receiving the line pressure. Hydraulic pressure supplied tothe first clutch C1 is supplied to the left side of the slider HC1 onthe drawing on a different surface from the surface receiving the linepressure. The hydraulic pressure for the first clutch C1 and the secondclutch C2 supplied to the slider HC1 is used as a reverse preparationpressure.

Also, a detent mechanism HC4 is disposed to the slider HC1 so that it isconfigured to prevent switching between the fixed state shown in FIG. 9Aand the reverse rotation preventing state shown in FIG. 9B unless theline pressure exceeds a predetermined pressure.

According to the hydraulic pressure control circuit HC, the two-wayclutch TW is switched to the fixed state as the slider HC1 is moved tothe left side on the drawing by opening the first valve HC2 and closingthe second valve HC3 so as to make the line pressure higher than orequal to a predetermined switching hydraulic pressure which is set basedon the pressure difference of the hydraulic pressure of the first clutchC1 and of the second clutch C2 and the engaging force of the detentmechanism HC4.

On the contrary, the two-way clutch TW is switched to the reverserotation preventing state as the slider HC1 is moved to the right sideof the drawing by closing the first valve HC2 and opening the secondvalve HC3 so as to make the line pressure higher than or equal to thepredetermined switching hydraulic pressure mentioned above.

Next, referring to FIGS. 1, 9A, 9B and 10 to 11, the control performedby the control part ECU of the automatic transmission TM when the drivesource ENG is stopped is described in detail.

As shown in FIG. 1, the vehicle on which the automatic transmission TMis mounted includes a shift lever SL that is capable of switching theshift position to any of the forward range, the neutral range and thereverse range and a drive source rotational frequency detector 6detecting the rotational frequency of the drive source ENG.

Also, the automatic transmission TM includes a hydraulic pressurecontrol circuit HC (the switching control circuit) switching the firstbrake B1 according to the instruction from the control part ECU.

The hydraulic pressure control circuit HC has a hydraulic pressuredetector HC5 (the driving force detector) detecting the hydraulicpressure supplied to the hydraulic pressure control circuit HC, ahydraulic pressure adjustment part HC6 including a hydraulic pressureadjustment valve capable of adjusting the hydraulic pressure of thehydraulic pressure control circuit HC based on information from thecontrol part ECU, and a stroke sensor HC7 (the switching part statedetector) recognizing the position of the slider HC1 (the switchingpart) (refer to FIGS. 9A and 9B).

The control part ECU receives information of the shift position from theshift lever SL, info nation of the rotational frequency of the drivesource ENG from the drive source rotational frequency detector 6,information of the hydraulic pressure from the hydraulic pressuredetector HC5 and information of the position of the slider HC1 from thestroke sensor HC7.

The control part ECU of the automatic transmission TM configured asabove performs a stop determination process of the drive source ENGshown in the flowchart of FIG. 10 when the control part ECU stops thedrive source ENG. This stop determination process is repeated at apredetermined time interval.

As shown in the flowchart of FIG. 10, firstly, the control part ECUcommences countdown of the timer for determining the stop of the drivesource ENG (FIG. 10/STEP 10).

Next, the control part ECU determines whether the rotational frequencyof the drive source ENG is less than or equal to a specified value ornot based on a signal from the drive source rotational frequencydetector 6 (FIG. 10/STEP 11).

The specified value in STEP 11 may be a value with which the drivesource ENG is determined to be stopped, such as 0 rpm or a significantlylow value, for example.

If the rotational frequency of the drive source ENG is determined to begreater than the specified value (NO at STEP 11), the control part ECUfinishes the process. The count of the timer is reset at the time.

On the contrary, if the rotational frequency of the drive source ENG isdetermined to be less than or equal to the specified value (YES at STEP11), the control part ECU determines whether a specified time has passedor not based on the countdown of the timer (FIG. 10/STEP 12).

If the specified time has not passed (NO at SPEP 12), the processreturns to STEP 11, and the control part ECU again determines whetherthe rotational frequency of the drive source ENG is less than or equalto the specified value or not.

On the contrary, if the specified time has passed (YES at STEP 12), thecontrol part ECU determines that the drive source ENG is stopped andfinishes the process (FIG. 10/STEP 13).

After finishing the above process, the control part ECU of the automatictransmission TM performs a switching process for the hydraulic pressurecontrol circuit HC (the switching control circuit) shown in theflowchart of FIG. 11.

As shown in the flowchart of FIG. 11, firstly, the control part ECUdetermines whether a signal from the hydraulic pressure detector HC5 isabnormal or not (FIG. 11/STEP 20).

For example, a signal indicating the hydraulic pressure from thehydraulic pressure detector HC5 indicates an abnormal value other than aspecified value in the case where the slider HC1 is positioned inbetween the position corresponding to the fixed state of the two-wayclutch TW shown in FIG. 9A and the position corresponding to the reverserotation preventing state of the two-way clutch TW shown in FIG. 9B,etc. Therefore, the control part ECU determines whether the slider HC1has moved to the specified position or not by STEP 20.

If the signal from the hydraulic pressure detector HC5 is determined notto be abnormal (NO at STEP 20), the control part ECU determines whethera signal from the stroke sensor HC7 is abnormal or not (FIG. 11/STEP21).

The control part ECU checks if it can recognize the position of theslider HC1 from the determination result of STEP 21.

If the signal from the hydraulic pressure detector HC5 is determined tobe abnormal (YES at STEP 20) or the signal from the stroke sensor HC7 isdetermined to be abnormal (YES at STEP 21), the control part ECUtransmits a signal for switching the two-way clutch TW to the reverserotation preventing state to the hydraulic pressure control circuit HCand finishes the process (FIG. 11/STEP 22).

For example, the state of the two-way clutch TW cannot be determined tobe in the state corresponding to the position of the slider HC1 in thecase where the slider HC1 is positioned in between the positioncorresponding to the fixed state of the two-way clutch shown in FIG. 9Aand the position corresponding to the reverse rotation preventing stateof the two-way clutch TW shown in FIG. 9B, etc.

Also, when the signal from the stroke sensor HC7 is abnormal, theposition of the slider HC1 cannot be accurately grasped, and the stateof the two-way clutch TW cannot be determined to be in the statecorresponding to the position of the slider HC1.

Therefore, if the signal from the hydraulic pressure detector HC5 or thestroke sensor HC7 is determined to be abnormal, the control part ECUtransmits a signal for switching the two-way clutch TW to the reverserotation preventing state to the hydraulic pressure control circuit HC.

By performing the control described above, driving force that forciblyswitches the two-way clutch TW to the fixed state is not applied whenthe drive source ENG is re-driven while the differential rotation isoccurring, regardless of whether the actual position of the slider HC1is at the position corresponding to the fixed state or the reverserotation preventing state of the two-way clutch TW.

The automatic transmission TM performs the process of STEPs 20 to 22based on the signal from the hydraulic pressure detector HC5 or thestroke sensor HC7. However, it is preferable that the automatictransmission TM performs the control for moving the slider HC1 to theposition corresponding to the reverse rotation preventing state (thereverse rotation prevention side) of the two-way clutch TW in the sameway when a signal indicating that there exists abnormality in theposition of the slider HC1 or that the position of the slider HC1 cannotbe recognized is received from other components.

On the contrary, if the signal from the stroke sensor HC7 is determinednot to be abnormal (NO at STEP 21), the control part ECU determineswhether the position of the slider HC1 matches with the position thecontrol part ECU instructed before the stop determination or not (FIG.11/STEP 23).

If the position of the slider HC1 matches with the position the controlpart ECU instructed (YES at STEP 23), the control part ECU finishes theprocess.

On the contrary, if the position of the slider HC1 does not match withthe position the control part ECU instructed (NO at STEP 23), thecontrol part ECU transmits a signal for switching the two-way clutch TWto the state corresponding to the actual position of the slider HC1 tothe hydraulic pressure control circuit HC, and finishes the process(FIG. 11/STEP 24).

If the drive source ENG is re-driven when the actual position of theslider HC1 corresponds to the reverse rotation preventing state of thetwo-way clutch TW and the position the control part ECU instructedcorresponds to the fixed state, the hydraulic pressure control circuitHC tries to switch the two-way clutch TW to the fixed state even if thedifferential rotation is occurring in the two-way clutch TW. As aresult, a large impact may be applied to the components of the two-wayclutch TW or the hydraulic pressure control circuit HC.

Also, if the drive source ENG is being re-driven when the actualposition of the slider HC1 corresponds to the fixed state of the two-wayclutch TW and the position the control part ECU instructed correspondsto the reverse rotation preventing state, the responsiveness may bedeteriorated because an operation to make the state of the slider HC1match with the state the control part ECU instructed is needed.

However, when the drive source ENG is determined to be in the stoppedstate, the control part ECU transmits a signal for switching the two-wayclutch TW to the state corresponding to the position of the slider HC1if the position of the slider HC1 does not correspond to the state thecontrol part ECU instructed before the drive source ENG is determined tobe in the stopped state. That is, the control part ECU determines theactual state of the hydraulic pressure control circuit HC, and instructsto make the state of the two-way clutch TW correspond to the actualstate of the hydraulic pressure control circuit HC if the actual statedoes not match with the state the control part ECU instructed.

Therefore, in the automatic transmission TM, the position of the sliderHC1 is not switched according to the instruction from the control partECU when the drive source ENG is re-driven because the actual positionof the slider HC1 (that is, the actual state of the two-way clutch TW)matches with the state of the two-way clutch TW the control part ECUinstructed.

As a result, the two-way clutch TW is not forcibly switched to the fixedstate while the differential rotation is occurring in the two-way clutchTW. Also, deterioration in the responsiveness after the drive source ENGis re-driven is suppressed.

Accordingly, the automatic transmission TM hardly has a breakage anddeterioration in the responsiveness when the drive source ENG isre-driven.

The embodiment depicted on the drawings has been described above, but,the present invention is not limited thereto.

For example, in the above embodiment, the process of STEPs 20 to 22 inthe switching process for the hydraulic pressure control circuit HC (theswitching control circuit) shown in the flowchart of FIG. 11 is aprocess for dealing with the case where the control part ECU cannotrecognize the position of the slider HC1 (the switching part).Therefore, STEPs 20 to 22 may be omitted if it is guaranteed that thecontrol unit can recognize the position of the switching part.

Also, the embodiment described above uses the hydraulic pressure controlcircuit HC as the switching control mechanism. That makes the slider HC1the switching part, the stroke sensor HC7 the switching part statedetector, and the hydraulic pressure detector HC5 the driving forcedetector. However, the switching control mechanism of the presentinvention is not limited to such a hydraulic pressure control circuit,and an electric circuit, etc. may be used as the switching controlmechanism.

Also, in the above embodiment, the automatic transmission TM isconfigured to be capable of changing speed in 10 gear positions.However, the present invention may be applied to any automatictransmission that is capable of changing speed in a plurality of gearpositions.

Also, in the above embodiment, the switching of the shift positions ismade by the shift lever operation. However, the switching method of theshift positions is not limited thereto, and, for example, it is possibleto configure to change the shift positions by pressing buttons, etc. Forexample, it is possible to configure to determine the selected shiftposition from a pressing signal of a button.

What is claimed is:
 1. An automatic transmission, comprising: an inputmember disposed inside a casing and rotated by a driving forcetransmitted from a drive source; a planetary gear mechanism, whereineach of which has a plurality of elements rotatable inside the casing; aplurality of engagement mechanisms switchable to a coupled state inwhich the elements are coupled to one another, or switchable to a fixedstate in which the elements are fixed to the casing, comprising: aswitching mechanism switchable between the fixed state and a reverserotation preventing state that allows a normal rotation and prevents areverse rotation of corresponding elements among the plurality ofelements; an output member outputting a rotation; a control partcontrolling the engagement mechanisms and recognizes a rotationalfrequency of the drive source; and a switching control circuit switchingthe engagement mechanism according to a signal from the control part,comprising a switching part switching the switching mechanism to thereverse rotation preventing state or the fixed state and a switchingpart state detector transmitting a signal indicating a state of theswitching part to the control part, wherein the automatic transmissionis configured to output a rotation of the input member from the outputmember while changing speed in a plurality of gear positions with theplanetary gear mechanism and the engagement mechanisms, and in the casewhere the drive source is determined to be in a stopped state by thecontrol part, if the state of the switching part does not correspond toa state that the control part instructed before the drive source isdetermined to be in the stopped state, the control part transmits asignal for switching the switching mechanism to a state corresponding tothe state of the switching part to the switching control circuit.
 2. Theautomatic transmission according to claim 1, wherein in the case wherethe drive source is determined to be in the stopped state by the controlpart, if the state of the switching part cannot be recognized, thecontrol part transmits a signal for switching the switching mechanism tothe reverse rotation preventing state to the switching control circuit.3. The automatic transmission according to claim 1, wherein theswitching control circuit further comprises a driving force detectordetecting a driving force to change the state of the switching part, andin the case where the drive source is determined to be in the stoppedstate by the control part, if the driving force is different from adriving force corresponding to the state of the switching part, thecontrol part transmits a signal for switching the switching mechanism tothe reverse rotation preventing state to the switching control circuit.4. The automatic transmission according to claim 2, wherein theswitching control circuit further comprises a driving force detectordetecting a driving force to change the state of the switching part, andin the case where the drive source is determined to be in the stoppedstate by the control part, if the driving force is different from adriving force corresponding to the state of the switching part, thecontrol part transmits a signal for switching the switching mechanism tothe reverse rotation preventing state to the switching control circuit.